Voice assistants do a small subset of the things you can already do easily on your phone. Competing with things you can already do easily on your phone is very hard; touch interfaces are extremely accessible, in many ways more accessible than voice. Current voice assistants only being able to do a small subset of that makes them not really very valuable.

And we aren't updating and rewriting all the world's software to expose its functionality to voice assistants because the voice assistant needs to be programmed to do each of those things. Each possible interaction must be planned and implemented invidually.

I think the bet is that we WILL be doing substantially that, updating and rewriting all the software, now that we can make them do things that are NOT easy to do with a phone or with a computer. And we can do so without designing every individual interaction; we can expose the building blocks and common interactions and LLMs may be able to map much more specific user desires onto those.